This invention relates generally to a monitor for onboard detection of fuel vapor leakage from an evaporative emission space of an automotive vehicle fuel system, and more particularly to a leak detection monitor for distinguishing between presence of a gross leak, presence of a small leak that is less than a gross leak, and absence of a leak.
A known on-board evaporative emission control system of an automotive vehicle comprises a vapor collection canister that collects volatile fuel vapors generated in the headspace of a fuel tank by the volatilization of liquid fuel in the tank and a purge valve for periodically purging fuel vapors to an intake manifold of the engine. A known type of purge valve, sometimes called a canister purge solenoid (or CPS) valve, comprises a solenoid actuator that is under the control of a microprocessor-based engine management system, sometimes referred to by various names, such as an engine management computer or an engine electronic control unit.
During conditions conducive to purging, evaporative emission space that is cooperatively defined primarily by the tank headspace and the canister is purged to the engine intake manifold through the canister purge valve. A CPS-type valve is opened by a signal from the engine management computer in an amount that allows intake manifold vacuum to draw fuel vapors that are present in the tank headspace and/or stored in the canister for entrainment with combustible mixture passing into the engine""s combustion chamber space at a rate consistent with engine operation so as to provide both acceptable vehicle driveability and an acceptable level of exhaust emissions.
Certain governmental regulations require that certain automotive vehicles powered by internal combustion engines which operate on volatile fuels such as gasoline, have evaporative emission control systems equipped with an on-board diagnostic capability for determining if a leak is present in the evaporative emission space. It has heretofore been proposed to make such a determination by temporarily creating a pressure condition in the evaporative emission space that is substantially different from the ambient atmospheric pressure, and then watching for a change in that substantially different pressure that is indicative of a leak.
Two known types of vapor leak detection systems for determining integrity of an evaporative emission space are a positive pressure system that performs a test by positively pressurizing an evaporative emission space; and a negative pressure (i.e. vacuum) system that performs a test by negatively pressurizing (i.e. drawing vacuum in) an evaporative emission space.
Some sources believe that meaningful leak detection testing can be performed without necessarily striving to obtain a measurement of effective leak size area. Accordingly, it has been proposed to monitor vapor pressure in an evaporative emission space over time, to detect the attainment, or non-attainment, of certain superatmospheric and subatmospheric thresholds, and to utilize the result to categorize the evaporative emission space as having one of: a gross leak, a small leak, or no leak.
One general aspect of the invention relates to a leak detection monitor for an on-board evaporative emission leak detection system that detects leakage from an evaporative emission space of a fuel system for an engine of an automotive vehicle, the leak detection monitor comprising: a housing enclosing an interior space communicated to atmosphere; a port for communication with the evaporative emission space; a vent valve that is selectively operable to a first state for opening the port to the interior space and thereby venting the evaporative emission space to atmosphere and to a second state for closing the port to the interior space and thereby not venting the evaporative emission space to atmosphere; an electric device for sensing pressure differential between the port and the interior space indicative of pressure in the evaporative emission space relative to atmosphere within a range that includes a predetermined positive pressure useful in making a determination about leakage from the evaporative emission space and a predetermined negative pressure useful in making a determination about leakage from the evaporative emission space, and providing a corresponding signal; and an actuator for causing the vent valve to be open when the engine is running and to be closed when the engine is not running.
Another aspect relates to a leak detection monitor for an on-board evaporative emission leak detection system that detects leakage from an evaporative emission space of a fuel system for an engine of an automotive vehicle, the leak detection monitor comprising: a housing enclosing an interior space; a movable wall dividing the interior space into a first chamber space and a second chamber space; a first port for communication to atmosphere and terminating within the second chamber space in a seat; a valve carried by the movable wall for selectively seating on and unseating from the seat to selectively open and close the second chamber space relative to the first port; a second port for communicating the second chamber space to the evaporative emission space; a third port for communicating the first chamber space to an intake system of the engine to selectively position the movable wall within the interior space to one position when the engine is running and to another position when the engine is not running; and an electric device for sensing pressure differential between the first port and the second port indicative of pressure in the evaporative emission space relative to atmosphere within a range that includes a predetermined positive pressure useful in making a determination about leakage from the evaporative emission space and a predetermined negative pressure useful in making a determination about leakage from the evaporative emission space, and providing a corresponding signal.
Still another aspect of the invention relates to a leak detection monitor for an on-board evaporative emission leak detection system that detects leakage from an evaporative emission space of a fuel system for an engine of an automotive vehicle, the leak detection monitor comprising: a housing enclosing an interior space; a first port for communicating the interior space to atmosphere; a second port for communicating the interior space to the evaporative emission space; an electric operated valve within the interior space for opening one of the ports to the interior space when the engine is running and for closing the one port to the interior space when the engine is not running; an electric device for sensing pressure differential between the first port and the second port indicative of pressure in the evaporative emission space relative to atmosphere within a range that includes a predetermined positive pressure useful in making a determination about leakage from the evaporative emission space and a predetermined negative pressure useful in making a determination about leakage from the evaporative emission space, and providing a corresponding signal.
Further aspects of the invention will be presented in the following drawings, detailed description, and claims.